In the processing of raw vegetables, for example, potatoes, it is the common practice to blanch the raw vegetables prior to the cooking and freezing operations. Blanching is usually required in the vegetable food processing industry to inactivate enzymes, to expel air and other gases which may be present in the food product, to remove sugar which may build up during storage by converting the sugar into starch and to remove harsh flavors and certain odors which may be present prior to cooking and freezing operations. Rapid cooling is usually required immediately after blanching in order to avoid overcooking and to prevent the growth of microorganisms which might otherwise occur during a slow cooling process.
Most prior art commercial vegetable processing blanchers have been designed of the immersion type wherein an elongated tank was filled with extremely hot water and the vegetables were carried through the immersion bath by employing a known transporting means, such as a conveyor or an auger. Other blanchers have employed steam nozzles in conjunction with the vegetable transporting means in order to effect rapid blanching by utilizing steam sprays above and/or below the conveyor.
The prior art immersion type blanchers have disadvantages inherent with any tank type design in that the bath water could not be satisfactorily circulated throughout the tank rapidly enough to maintain substantially even temperatures from front to back. The introduction of the vegetables to be blanched at one end of the tank had a quenching effect at the inlet end whereby the bath water temperature could not be maintained at the inlet end substantially the same as in the downstream areas of the bath. During blanching operations, the bath tended to become stagnated wherein the water could not be continuously filtered. Additionally, the natural sugars in the vegetables tend to form starches. The immersion type blanchers were incapable of effectively removing the starch from the surface of the vegetables due to the quiescent nature of the bath water. All of this has generally resulted in a non-uniform final product with inherent, serious quality control problems.